#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(n);++i)
#define all(a) (a).begin(),(a).end()
using namespace std;
typedef long long ll;

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	ll l;
	cin >> l;

	vector<ll> dp(l + 2);
	ll a = 1;

	dp[3] = 1;

	for (ll i = 5; i <= l; i += 2) {
		dp[i] = dp[i - 2] + a + 2;
		a += 2;
	}

	cout << dp[l] << endl;
	return 0;
}